1. Field of the Invention
The present invention relates to a corner reduction device for rolling equipment for reducing side corners of a material by the use of corner rolls, a control device thereof, and a method of rolling the material by the use of these devices.
2. Description of the Related Art
Generally there is a necessity of performing a roughing process prior to a finish rolling process in order to produce rolled plates such as hot-rolled slabs by rolling to specific width and thickness.
In conventional equipment for performing the aforesaid roughing process, as schematically shown as one example in FIG. 1, rolling equipment 3 comprising an edging mill (edger) 1 and a horizontal mill (mill) 2 is arranged in multiple stages along a pass line L, and a carrying table 5 having a multitude of carrying rolls (table rolls) 4 arranged in both the front and rear positions of each of the rolling equipment 3. Furthermore, side guides 6 so formed as to avoid interference of each carrying roll 4 are arranged on the right and left sides of the pass line L, facing each other, above the carrying table 5. On the back surface of each carrying table 5, a cylinder 7 as a space controlling device is provided. A material 8 such as a slab to be conveyed on the carrying table 5 is guided to the rolling equipment 3 while its position is being restricted by the right and left side guides 6, then being repetitively rolled for reduction to specific width and thickness by the edging mills 1 and the horizontal mills 2. A reference numeral 9 denotes right and left table frames constituting the carrying table 5, and a reference numeral 10 expresses a bearing of the carrying roll 4.
In this roughing process, generally, a material is passed through the horizontal mill and the edging mill a plurality of times to produce a sheet bar. It is known that a slab 8 (a material to be rolled) shown in the top view of FIG. 2A, when horizontally rolled in the reverse pass of the roughing process as shown in the middle view of FIG. 2A, spreads in the direction of width, causing the side faces of the material to be subjected to bulging. Subsequently, with the edging of the side faces 8E of the slab 8 as shown in the bottom view of FIG. 2A, the corners 8C of the side faces of the material curve around towards the material surface. Consequently, the corners 8C are not fully reduced by the rolls as compared with other portions of the material, resulting in insufficient smoothing of wrinkled or cracked portions. The corners 8C of the side faces of the material curve around towards the material surface, producing a defect in the side edges of products. In the event of such a surface defect, the side edges of the material must be cut off, thereby resulting in a worsened yield.
Also, in rolling a relatively narrow and thick material, for example a slab for thick plate, by the above-described rolling equipment, with the repetition of rolling the slab 8 down to a sheet like a sheet bar in both directions of width and thickness by the edging mill 1 and the horizontal mill 2, there occurs an edge overlap 8L at edges on both sides of the slab 8 as shown in FIG. 3. More specifically, as shown in FIG. 2B, edging in the normal pass causes spreads in the upper and lower surface of the slab 8, which causes the overlap 8L in the subsequent horizontal rolling. The edge overlap 8L portion must be cut off in a later process, which will consequently become a cause to lower the yield of steel products.
In the meantime, a method for improving the quality of side face corner portions 8C of the slab 8 by carrying out the reduction of the side face corner portions 8C of the slab (material) 8 by the use of a caliber roll 11 as shown in FIG. 4A and FIG. 4B has been disclosed in Japanese Patent Laid-Open No. Sho 53-28542. Also disclosed in Japanese Patent Laid-Open No. Hei 2-25202 is a method, as shown in FIG. 5, for removing the side face corner portions of the slab 8 by using a grinding or turning device 12 annexed to the rolling mill 3. Furthermore in Japanese Patent Laid-Open No. Sho 63-161803 is proposed a method for rolling the corner portions by means of the caliber rolls 11 as shown in FIG. 4 and corner rolls 12 each having an inclined shaft center as shown in FIG. 6. In FIG. 6, a reference numeral 13 denotes a hydraulic cylinder for pressing with the corner rolls.
However, the prior art technique disclosed in Japanese Patent Laid-Open No. Sho 53-28542 has the following disadvantages:
(a) Abrasion will occur because of different peripheral speeds of the caliber roll 11 between the end positions 8D and 8E of the corner portion 8C shown in FIG. 4A.
(b) No substantial effect will be obtainable in case of a different thickness of the slab 8.
Further, the prior art technique disclosed in Japanese Patent Laid-Open No. Hei 2-25202 has the following disadvantages:
(c) Deteriorated yield will result with the removal of a defect area.
(d) It is hard to follow up a change in material width.
Also the prior art technique disclosed in Japanese Patent Laid-Open No. Sho 63-16803 has the following disadvantages:
(e) Abrasion will occur in the caliber roll 11 due to a difference in the peripheral speeds of the caliber roll.
(f) The corner roll 12 rolls linearly, resulting in a large rolling stroke and a very large equipment.
(g) The corner roll 12 is required to operate correspondingly to changes in material width, and therefore a width controlling device will be needed separately from a rolling mechanism, requiring a larger cost of equipment.
The use of corner rolls for rolling slab corners has been disclosed also in Japanese Patent Laid-Open Nos. Sho 49-91944 and Sho 63-60003, but has the same disadvantage as the corner rolls in Japanese Patent Laid-Open No. Sho 63-16803.
Furthermore, the slab 8 to be rolled at corners is not necessarily conveyed in a horizontal state along the pass line L; and therefore it is possible that there will occur waviness at the side edges or a warp in a cross direction (C warp), or a warp in the longitudinal direction (camber). Particularly, in the case of broadside rolling of a thin slab, uneven rolling reduction of the upper and lower corners and an increased C warp were likely to occur.